I sold my first A3000 which was my third Amiga to buy a Xbox. I loved that machine and really do miss it. I've replaced it but the one I have now isn't the same. I had a choice to sell my A2000 or the A3000. I kept the A2000 for two reasons. It was technically faster than the A3000 (Fusion 40 28Mhz installed in the A2000) and it was my first Amiga.
My runner up regret was selling my CD32 w/ SX-1 and FMV card. Had lots of fun with that setup.
One a non-amiga regret note I threw out a SX-64 in a move when I lived in NYC. I just had no space left. That one also still pains me today.